This invention relates in general to dental radiography and more specifically to a collimating device which finds particular utility in cephalometric radiography.
In dental radiography, it is common for the patient to be given both intra-oral and cephalometric (extra-oral) X-rays. In the intra-oral process, the X-ray sensitive film is located within the mouth, while it is held in position behind the head in the extra-oral process. It has been the usual practice in the past to employ a single device known as a position indicating device (PID) or "cone" for both the intra-oral and extra-oral processes. The PID is essentially a lead lined cylindrical tube which attaches to the X-ray generator. The X-rays pass through a lead diaphragm in the PID and are thereby formed into a circular beam which is directed toward the patient and the X-ray sensitive film.
While the PID continues to be widely used for intra-oral X-rays, recent governmental regulations and general safety considerations have made it necessary to discontinue its use in the extra-oral process. These regulations require that the beam used in the taking of cephalometric X-rays conform in size and shape with the rectangular cassettes in which the X-ray film is contained. The present invention is directed to a collimating device which attaches to the PID in order to adapt it for use with the rectangular cassettes that are used in cephalometric radiography.
There have been attempts made to provide box-type attachments for the PID in order to form a rectangular beam. However, the devices that have been developed have not been entirely satisfactory, primarily because of their cost and complexity, and also because of the difficulty involved in attaching them to and removing them from the PID. Moreover, these devices often provide a beam which is either too large or too small when it reaches the patient and cassette. Each time the collimating device is attached to the PID, its rectangular aperture must be located exactly the same distance from the X-ray generator in order to provide a beam which is of the proper size when it reaches the patient, who is located a standard distance (60 inches) from the X-ray machine. However, existing collimators of this type are unable to be located with the required precision each time they are attached to the PID, and consequently they do not always collimate the beam accurately enough and with sufficient repeatability to satisfy government regulations or to conform with general safety standards.
It is an important object of the present invention to provide a collimating device which is able to be quickly and easily attached to a PID and which functions to produce a rectangular X-ray beam that conforms accurately in size, shape, and orientation with a standard film cassette of the type used in cephalometric radiography.
Another important object of the invention is to provide a collimating device in which the rectangular opening that collimates the beam is located at exactly the same distance from the X-ray generator and in the same rotative position each time the device is attached to the PID. This is a significant feature of the invention because it assures that the beam will always coincide precisely with the cassette in size and shape.
Yet another object of the invention is to provide a collimating device of the character described which may be used with existing X-ray generators of various types.
A further object of the invention is to provide a collimating device of the character described which effectively shields against X-ray leakage.
An additional object of the invention is to provide a collimating device of the character described which is constructed simply and economically and which operates safely.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.